In the manufacture of highly absorbent materials and structures for use in personal care products such as diapers, feminine hygiene products and bandages, there is a continual effort to improve performance characteristics. Although the structure of these personal care products have many components, in many instances the in-use performance of the product is directly related to the characteristics of the absorbent composite it contains. Accordingly, manufacturers of these products strive to find ways of improving the properties of the absorbent composite in order to reduce leakage while providing comfort to a wearer.
One means of reducing the leakage and increasing absorbency has been the extensive use of superabsorbent materials. Recent trends in commercial diaper design have been to use more superabsorbent materials and less fiber in order to make the product thinner. However, products with a high content of superabsorbent materials still leak, as many absorbent materials are unable to absorb a liquid at the rate at which the liquid is applied to the absorbent composite during use. The addition of fibrous material to the absorbent composite decreases the amount of leakage of an absorbent composite by temporarily holding the liquid until the superabsorbent material absorbs it. Fibers also serve to separate the particles of superabsorbent material to avoid or reduce gel-blocking. As used herein, the term “gel-blocking” refers to a situation wherein particles of superabsorbent material deform during swelling and block the interstitial spaces between the particles, or between the particles and the fibers, thus preventing the flow of liquid through the interstitial spaces. Even when fibrous material is incorporated into an absorbent composite, a poor choice of a superabsorbent material, especially one which exhibits gel-blocking behavior within the absorbent composite, results in poor liquid handling properties in the life cycle of the absorbent composite. Consequently, the choice of absorbent composite materials greatly affects the in-use absorbency and leakage of the absorbent product. To reduce leakage during the life cycle of the product, it is desirable to maintain the level of intake performance of the absorbent composite throughout the life of the product.
Polymeric foams, such as those described in U.S. Pat. No. 5,397,316 to LaVon et al., have many advantages in absorbent products. High internal phase emulsion foams (HIPE), such as those described in U.S. Pat. No. 5,331,015, have been developed in an effort to create absorbent polymeric foams with enhanced fluid intake. These HIPE foams are prepared by polymerizing water-in-oil emulsions having a relatively small amount of an oil phase and a relatively greater amount of a water phase. However, this type of HIPE foam is expensive and has poor wettability and no swelling capability thereby creating problems with its use as a superabsorbent composite. Additionally inverse HIPE (I-HIPE) foams have been developed using oil-in-water (O/W) emulsion systems. However, there has been difficulty in extracting the oil phase that may be entrapped by the polymer matrix after polymerization.
What is needed is an absorbent composite having improved composite properties. What is also needed is an absorbent composite, capable of mass production which exhibits an improved fluid intake rate, and/or fluid intake of multiple insults over the life of the composite.